Spirometer



Oct. 27, 1964 M. J. REINERT ETAL SPIROMETER 4 Sheets-Sheet 1 Filed March 29, 1961 T W W m w Y B 5 m m C:

ATTORNEY.

Oct. 27, 1964 M. J. REINERT ETAL 3,154,058

SPIROMETER Filed March 29, 1961 4 Sheets-Sheet 2 INVENTORS. MILTON J. REINERT DANIEL. A. TALONN ATTORNEY.

Oct. 27, 196 M. J. REINERT ETAL 3,154,068

SPIROMETER 4 Sheets-Sheet 5 Filed March 29, 1961 l l INVENTORS, H66 4 MILTON J. REINERT BY DANIEL A.TALONN ATTORNEY Oct. 27, 1964 3,154,068

M. J. REINERT ETAL SPIROMETER Filed March 29, 1961 4 Sheets-Sheet 4 INVENTORS, MILTON J. REINERT DANIEL A. TALONN ATTORNEY.

United States Patent 3,154,068 SPTEROMETER Milton 5. Reinert, Ferguson, and Daniel A. Talorm, St. Louis, Ma, assignors to Med-Science Electronics, inc, a corporation of Missouri Filed Mar. 29, 1961, Ser. No. 99,199 7 Claims. (til. 1282.08)

One of the objects of this invention is to provide a spirometer which does not utilize a water seal.

Another object of this invention is to provide a spirometer which allows a patient to breath in a normal, unloaded fashion. Measurements can then be made of the breathing characteristics without having the measuring apparatus aiiect those characteristics and thereby disturbing the results.

Previous to this invention the spirometer consisted of an inverted bucket floating in a water bath, and sealed by the water. Breathing into the bucket raised the bucket, and breathing from the bucket lowered the bucket. The weight of the bucket however loads the breathing and the result is not normal breathing. The solution to this has been to counterbalance the weight of the bucket. While this makes the bucket less of a resistive load, the inertia of the resultant system is such that the frequency response of the measuring device is compromised. The bucket and counterbalance simply will not follow rapid breathing.

Another object of the invention is to provide a high dynamics spirometer. The instrument is designed to have small travel of the parts in motion corresponding to large volume differentials or changes in volume. Therefore large volumetric accelerations will correspond to small linear accelerations. Since for a given mass in motion, the lower the accelerations, the higher will be the frequency response.

Another object of the invention is to provide a spirometer which will offer all known functions of previous spirometers, and at the same time provide an electrical readout of both volume changes and flow changes. These two measurements are entirely independent. Previous to this invention, no patient-driven spirometer has been capable of independent readout of volume changes and flow changes.

The low linear accelerations result in small forces required to actuate the moving elements. Since the patients lungs in mechanical spirometry are required to generate the forces to drive the spirometer, it can readily be seen that the lower linear accelerations result in lower forces in the lungs to drive the spirometer. Thus the patients breathing is more nearly normal during the process of measurement. The eiiect is magnified at the point of higher dynamics, such as rapid breathing and coughing.

In an ordinary spirometer, a patient coughing not only is affected physiologically by the higher forces of the ordinary spirometer, but the actual cough is recorded subject to the errors of the instrument at high frequencies.

A further object of the invention is to provide a spirometer in which the ambient pressures Within the spirometer and the patients lungs remain as close to atmospheric pressure as possible. Thus the patient does not have the feeling that something is impeding his breath, which is the case in the ordinary spirometer. The conventional spirometer is sealed by a water bath. Since the water lies in a horizontal plane, the motion of the spirometer bucket is restricted to a vertical plane. Thus if the bucket is not counterbalanced, its weight will increase the pressure in the spirometer. Our new spirometer has been designed without a water seal, therefore the motion of the spirometers moving elements has been restricted to the horizontal plane. The weight of the moving member is supported entirely by hinges and does not con- BJM MS Fatented Oct. 27, 1964 tribute to any pressure changes of the gas or air inside the spirometer.

further object of the invention is to provide a bellows or compliant member between the relatively moving members of the spirometer to act as a seal, which otters as little resistance to motion as possible.

An additional object of the invention is to provide readout means in the form of two electrical signals proportional to volume and flow changes respectively. In the form described the transducers for these two readouts offer infinite resolution and low force requirements.

in the drawings:

FIG. 1 consists of a side elevation of the spirometer, partially broken away to show internal construction;

P16. 2 consists of a perspective view of the spirometer with a recording pen attached;

FIG. 3 is a detail view of the construction of a corner of the bellows;

FIG. 4- is a detail view of a pivot assembly;

FIG. 5 is the plan view of the bellows construction;

FIG. 6 is a perspective view of a corner of the bellows; and

FIG. 7 is a schematic of the electrical circuitry.

In FIG. 1, numeral 1 is given to the stationary panshaped member and 2 is the movable pan-shaped member. These members are preferably in the form of large square flat pan members having four edges bent vertical to the plane of the pan member. Pan member 2 is pivoted to pan member 1 by two pivot assemblies 3 disposed on any mutual edge of the pan members. For illustration the pivot 3 is shown at the top edge of the pan members.

The pan assembly is mounted in a vertical position by means of the support stand 4 which has a foot section 5 resting on any horizontal surface and a support section bolted by bolt 6 to the stationary pan member 1. A bellows 7 made of plastic in a manner to be illustrated later is sealed to the edges of both pan members by means of metal strips 8 and bolts 9.

Pan members 1 and 2, together with the bellows 7 form a sealed chamber. Communication to this chamber is made through a centrally located port or hole in pan member 1 around which is welded the end of pipe 10. Needless to say the weldment and all the bolts and metal screws through the pan members must be sealed tightly.

Both pan members are stiffened to obtain the rigidity required in a spirometer. Pan member 1 is stiflened by the baffle plate 11 mounted a short distance away from the pan member 1 by means of spacers 12 and bolts 13. Baflie plate 11 serves the function of breaking up or dispersing the incoming wave fronts of the air masses. Baflle plate Iill serves also to reduce the dead space in the spirometer chamber. Pan member 2 is stilfened by means of a pair of guy wires 14, also shown in FIG. 2. In FIG. 3 it will be seen that the guy terminates at a bolt 15 in a turnbuckle arrangement consisting of a nut 16 on the threaded end of the guy wire. At the center of the pan 2, the guy wire passes through the trussing block 17. The two crossed guy wires 14, by being tightened at their turnbuckle ends exert a combined force through the trussing block which renders the pan member 2 taut.

The box 18 is mounted rigidly to the foot section 5 of the support stand 4 and to the lower edge of the stationary pan member 1 and thereby contributes to rigidizing the support structure and the pan member 1. The box 18 contains the two transducers 19, 19' which are provided with movable cores 20 and 20'. Each core is connected to the lower edge of the movable pan member 2 by a thin rod 21, 21', and the bracket 22. The rod 21, 21 is fixed at each end and flexible therebetween.

The box 18 also contains the associated circuitry shown in FIGURE 7. On the back side of the box are mounted the calibration button switches 23 and the terminals 24.

The bellows 7 will be seen in FIG. 3 to be attached to the pan member 2 by means of pressure applied by a metal strip 8 through a cushion of rubber 25. The bolt g passes through the strip 8, the cushion 25, the bellows 7 and the pan member edge, and is held in sealed engagement with a nut.

In FIG. 4 is shown the pivot assembly 3, which consists of a bracket 26 integral with pan member 1 and bracket 27 integral with pan member 2. Bracket 26 carries an integral shaft 28 upon which is rotatably mounted the ball bearing 29 which is integral with bracket 27. Thus pan member 2 can pivot upon pan member 1 with minimal friction. For the purpose of illustration the pivot assemblies are shown in FIG. 1 to be located on the top horizontal edges of the pan members I and 2. It will be seen that the entire apparatus can be rotated in space 90 or 180 through the vertical plane and the pivot assemblies will then be positioned along one of the vertical edges or along the bottom edge.

The construction of the bellows 7 is shown in FIG. 5. A thin sheet 30 of a flexible material which is not porous to air, such as plastic or rubber or paper has fixed to it ribs 31 of a fiat, stiff reinforcing material. The ribs can be vinyl plastic and the sheet can be vinyl in which case the ribs can be affixed to the sheet by solvent action, by gluing or by heat sealing. The ribs 31 are seen to be all of the same configuration except the ones on the edge. There the ribs 32 and 33 are shown to be of half width and to have the configurations illustrated. It will be seen that the ribs 32 and 33 are approximately trapezoidal in shape. However all the other ribs 31 are provided with ends having a shape which is a straight-line approximation of a parabola. The bellows which is a strip has its ends brought together and sealed or glued together so that a sleeve is formed. This sleeve assumes a rectangular shape corresponding to the shape shown in FIG. 2, said rectangular shape being defined by the folding enforced by the rigidizing ribs 31, 32, 33.

The purpose of the arrangement of the ribs 31, 32 and 33 on the plastic sheet 35) is to obtain the folded configuration illustrated in FIG. 6. Here it will be seen that all the expansion of the bellows 7 is confined to the hinge folds, that is the folds 34, between the ribs 31.

The ribs 31 do not show in FIG. 6 since they are on the underside of the sheet 30. This construction can be seen to confine motion of the bellows during expansion and contraction of the bellows to a hinging or bending motion at the folds 34 and precludes any rolling motion of the material of the thin sheet 30. This serves the dual purposes of reducing wear and tear on the thin sheet 30 and also reducing the forces required to expand or contract the bellows 7. The action of the sheet 30 is limited to a pure bending of the material and there are no shearing stresses exerted.

It will be noted that for a ten-litre spirometer the expansion of the bellows and the relative travel of pan members edges is of the order of five centimeters whereas the pan members measure sixty-five centimeters on a side. It will be seen that a movement of 2%. millimeters or only one-tenth of an inch corresponds to the size of an ordinary adult breath, i.e., 500 cubic centimeters. As a consequence the inertial loading on the patients lungs is low and the dynamic response of the instrument is high. The five centimeter travel is the maximum travel and amounts to the ten liter volume but is less than five degrees of arc. This is contra to the previous teaching of the art and is responsible for the remarkably low inertial loading which has previously not been possible in mechanical spirometers of the type.

The ribs 31, 32 and 33 confine the thin sheet 3t) to assume the proper shape shown in FIG. 6 and in addition serve to reinforce the bellows to prevent its caving in or blowing out with sudden changes in pressure.

The circuitry is shown in FIG. 7. It consists of a power supply in the lower portion of the figure, a Volume signal circuit in the middle portion of the figure and a flow signal circuit at the top portion.

The power supply consists of a plug 35, switch 36, and fuse 37, together with a constant voltage isolation transformer 3%. The 60 cycle alternating current of transformer 33 is passed through rectifier 39 and filtered by the two resistors 4t), 41 and the two capacitors 42, 43 to provide a direct current voltage across the potentiometers 44, 45. The wiper 46 on potentiometer 44 taps a voltage which may be adjusted in order to produce a calibrating flow signal. The wiper 47 on potentiometer taps a voltage which may be adjusted in order to produce a calibrating volume signal.

The A.C. output of isolating transformer 38 energizes the primary coil 43 of the volume transducer. The coil 48, together with coils as and form a linear variable differential transformer in which the position of the core 26 determines the flux linkages between the primary coil 48 and the two secondary coils 49 and 50. The AC. voltage induced in coil 49 appears across terminals 51 and 52 of the full-wave rectifier bridge formed of four rectifiers 53. A corresponding DC. voltage appears across the terminals 54 and 55. This voltage is filtered through the network consisting of capacitor 56 and resistors 57 and 53 and appears across resistor 58.

The AC. voltage induced in coil 50 appears across terminals 59 and 66 of the full-wave rectifier bridge formed of four rectifiers 61. A corresponding D.C. voltage appears across the terminals 62 and 63. This voltage is filtered through the network consisting of capacitor 64- and resistors 65 and 66 and appears across resistor 66. The polarity of the two voltages across resistors 58 and 66 is chosen such that they are in bucking arrangement. The resulting difierential output appears across terminals 24. This voltage is proportional to the displacement of core 20, which is seen in FIG. 1 to be connected to the bracket 22 of pan member 2. It will later be shown that this voltage signal is proportional to the volume contained in the spirometer.

The flow circuit at the top of the FIG. 7 consists of core 2th, a permanent magnet, which moves relative to the coil 67, thus generating in that coil a DC. voltage which is proportional to the velocity of the core 20. This core 2% is connected to the same bracket 22 as 20 above, and the identical movements of the two cores 20, 2.6 are indicated by the dotted line between them in FIG. 7. The generated voltage of coil 67 appears across the terminals 24'. It will later be shown that this signal is proportional to the flow.

The voltage appearing on wiper 47 is connected to terminal 68 of button switch 23. When the button switch 23 is in the position shown, which is its normal position, the voltage appearing across terminals 24- corresponds to the output of the transducer 19, which is composed of the coil 48, core Ztl, and coils 49 and 50. When depressed the button switch is as shown in the dotted line position, in which case the voltage appearing across the terminals 24 will be increased by the voltage tapped by the wiper 47. Normally the potentiometer 45 is adjusted to give a voltage at wiper 47 corresponding to the signal which would be produced by the transducer 19 when the volume change is one liter. This voltage change is used as a calibrating signal for one liter. When used on a readout instrument such as a recorder this calibrating signal will serve as a standard to determine the scale of the data.

In a similar manner wiper 46 of the potentiometer 44 is connected to terminal 69 of push button 23'. In the normal position, as shown in FIG. 7, the voltage appearing across terminals 24' corresponds to the output of the transducer 19', which consists of core 20 and coil 67. When the button switch 23' is depressed, as shown by the dotted line, the voltage tapped by wiper 46 will be added to the output voltage of transducer 19', the sum of both appearing across terminals 24'. Normally the potentiometer 44 is adjusted to give a voltage at wiper 46 corresponding to a flow signal which would be produced by the transducer 19' for a flow of one liter per second. This voltage change is used as a calibrating signal as above.

In operation, an ordinary facial mask and tubing common to the art of spirometry are attached to a patient, connecting the patients mouth with the pipe of the apparatus. The air in the patients lungs and the air in the connecting tubing and the air in the apparatus are now contained in a hermetically sealed system. For long term measurements the ordinary technique of inserting a C0 absorber in the connecting tubing is employed to prevent CO buildup.

The patient is enabled to breath by exchanging air between his lungs and the spirometer apparatus. When the patient exhales, the apparatus volume will increase, because the pan member 2 will move outward and away from .pan member 1 in FIG. 1. Similarly inhalation will produce a decrease in volume and a movement of pan member 2 toward pan member 1. It therefore can be seen that the volume changes in the spirometer chamber are equal and opposite to those occurring in the patients lungs at any instant. As described above since the instrument has low inertia and low resistance, it will follow any such volume change faithfully.

Since the bellows material cannot stretch and all the other dimensions of the spirometer chamber are fixed, all volume change of the spirometer chamber is absorbed by a relative motion of pan member 2 with respect to pan member 1. Pan member 2 is pivotally mounted upon pan member 1, the motion of the bottom edge of pan member 2, and the bracket 22 is proportional to the change in volume. Core 20 is connected to bracket 22 and its position corresponds to the specific volume contained in the spirometer chamber.

From the description of the volume portion of the circuit in FIG. 7 it has been shown that the voltage appearing across terminals 24 corresponds to the position of core 20. Hence said voltage also corresponds to the instantaneous volume of the apparatus.

Since the volume of the chamber is directly proportional to the area of the pan member times the linear displacement of the bracket 22 from pan member 1, the derivative of the volume with respect to time is proportional to the derivative of the linear displacement. Hence the velocity of the bracket 22 is directly proportional to the fiow rate of gas into or out of the chamber. Core 20' is attached to the bracket 22 and therefore its velocity is proportional to the flow rate of the gas.

As has been shown previously, the voltage appearing across terminals 24 is proportional to the velocity of the core 20'. Now it will be seen that the above voltage signal corresponds to the fiow rate of the gas.

Thus it will be seen that independent electrical signals proportional to the volume and the flow rate of the gas in the spirometer are here obtained directly. This produces a big advantage over previous spirometry in which for instance flow rates have been obtained by such indirect methods as using a pneumotachograph, or by differentiating the volume changes. Volume has even been obtained by integrating the pneumotachograph signals. These methods suffer from various disadvantages such as poor resolution and high background noise, and drift problems. Our instrument contrariwise has relatively infinite resolution, low noise and no drift.

An alternative arrangement we employ consists of a mechanical readout. In this case the bracket 22 of FIG. 2 carries an ordinary recorder pen 70 with its ink reservoir. The pen rests on a chart drum '71 which rotates as it is driven by a motor not shown. Movement of the pen member 2 moves the pen 70 and records the movement on the rotating drum '71.

Although this invention has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is therefore to be limited only as indicated by the scope of the appended claims.

We claim:

1. A spirometer for testing a patients lung consisting of two vertically disposed rectangular pan members, one

stationary and the other pivoted upon and suspended from the first, a flexible bellows between said pan members and sealed to said pan members to form the spirometer chamber, a baflle in the form of a plate mounted between said pan members and affixed to the stationary pan member to break up and disperse incoming Wave fronts of air masses, an open tube through said stationary pan member for connection with the patients lungs, rigidizing ribs integral with said bellows to prevent deformation of said bellows, and folds in said bellows between said rigidizing ribs to limit the motion of said bellows to expansion by hinge action at said folds.

2. A spirometer for testing a patients lungs, consisting of two vertically disposed rectangular pan members, one stationary and the other pivotally suspended upon and movable with respect to the first, said pan members measuring 65 centimeters on each side, a flexible bellows between said pan members and sealed to said pan members to form the spirometer chamber, a bafile in the form of a plate mounted between said pan members and afiixed to the stationary pan member to rigidize said pan member and to break up and disperse incoming wave fronts of air masses, a pair of guy Wires on said movable pan member to rigidize said movable pan member, an open tube through said stationary pan member to connect with the patients lungs with the spirometer chamber formed by said pan members and said bellows, rigidizing ribs integral with said bellows to prevent deformation of said bellows, and folds in said bellows between said rigidizing ribs to limit the motion of said bellows to expansion by hinge action at said folds, the maximum movement of said pivotably suspended pan member with respect to the stationary pan member being less than 5 degrees of are.

3. A spirometer for testing a patients lungs consisting of two large rigid vertically disposed rectangular pan members measuring 65 centimeters on each side, one stationary and the other hingedly suspended from the first and movable with respect thereto, a flexible bellows between said pan members and sealed at its edges to said pan members to form an expansible chamber, said bellows limited to a maximum expansion on its most expandable side of five centimeters, an open tube through said stationary pan member to communicate with the patients lung, the expansion of said bellows and the concomitant travel of hingedly suspended pan member with respect to the stationary pan member being small with respect to the size of said pan members the maximum travel being less than five degrees of are.

4. A spirometer for testing a patients lungs consisting of two rigid vertically disposed rectangular pan members measuring 65 centimeters on each side, one stationary and the other hingedly suspended upon the first and movable with respect thereto, a flexible bellows between said pan members consisting of a sleeve of plastic formed into a rectangular shape, said bellows limited to a maximum expansion of five centimeters, rigidizing ribs in the form of strips integrally afiixed to said sleeve, and compliant folds in said bellows between said rigidizing ribs to limit the motion of said bellows to expansion by hinge action at said folds.

5. A spirometer for testing a patients lung consisting of two large rigid vertically disposed rectangular pan members, one stationary and the other hingedly suspended from the first and movable with respect thereto, a relatively narrow flexible bellows between said pan members and sealed at its edges to said pan members to form an expansible chamber, an open tube through said stationary pan member to communicate with the patients lungs, the expansion of said bellows and the concomitant travel of the hingedly suspended pan member with respect to the stationary pan member being small with respect to the size of said pan members, a volume transducer consisting of a linear variable differential transformer provided with a movable core and associated stator windings, said core being mounted upon the movable pan member and said windings being affixed to the stationary pan member, so that the relative motion of the pan members alters the relative position of the core within said windings to generate a voltage directly proportional to the volume of gas moved by said patients lungs, a power supply for the transformer, and a demodulator for the output of said transformer.

6. A spirometer for testing a patients lungs consisting of two large rigid vertically disposed rectangular pan members, one stationary and the second suspended from the first and movable with respect thereto, a narrow flexible bellows between said pan members and sealed at its edges to said pan members to form an expansible chamber, an open tube through said stationary pan member to communicate with the patients lungs, the expansion of said bellows and the concomitant travel of the second pan member with respect to the stationary pan member being of the order of one-tenth the size of said pan members, a flow transducer consisting of a permanent magnet core and a Winding, and the core being mounted upon the movable pan member and said winding being atfixed to the stationary pan member, so that the relative motion of the pan members generates a voltage in said winding directly proportional to the flow rate of gas to and from the patients lungs.

7. A spirometer for testing a patients lungs consisting of two large rigid vertical rectangular pan members, one stationary and the other hingedly mounted upon and suspended from the first and movable with respect thereto, a flexible bellows between said pan members and sealed at its edges to said pan members to form an expansible chamber, an open tube through said stationary pan member to communicate between the patients lungs and said expansible chamber, the travel of the hingedly mounted pan member with respect to the stationary pan member being approximately one-tenth the dimensions of said pan members, a mechanical recorder consisting of a recorder pen mounted on the movable pan member, and a rotating chart drum whose rotation is transverse to the movement of the pan member and the pen for recording said movement.

References (Iited in the file of this patent UNITED STATES PATENTS 2,180,057 Jones Nov, 14, 1939 2,923,290 Elam Feb. 2, 1960 2,933,082 Billin Apr. 19, 1960 2,999,495 Shipley Sept. 12, 1961 3,006,336 Burlis Oct. 31, 1961 3,021,839 Marsh Feb. 20, 1962 3,026,868 Weinberg Mar. 27, 1962 FOREIGN PATENTS 557,606 Italy Feb. 18, 1957 

1. A SPIROMETER FOR TESTING A PATIENT''S LUNG CONSISTING OF TWO VERTICALLY DISPOSED RECTANGULAR PAN MEMBERS, ONE STATIONARY AND THE OTHER PIVOTED UPON AND SUSPENDED FROM THE FIRST, A FLEXIBLE BELLOWS BETWEEN SAID PAN MEMBERS AND SEALED TO SAID PAN MEMBERS TO FORM THE SPIROMETER CHAMBER, A BAFFLE IN THE FORM OF A PLATE MOUNTED BETWEEN SAID PAN MEMBERS AND AFFIXED TO THE STATIONARY PAN MEMBER TO BREAK UP AND DISPERSE INCOMING WAVE FRONTS OF AIR MASSES, AN OPEN TUBE THROUGH SAID STATIONARY PAN MEMBER FOR CONNECTION WITH THE PATIENT''S LUNGS, RIGIDIZING RIBS INTEGRAL WITH SAID BELLOWS TO PREVENT DEFORMATION OF SAID BELLOWS, AND FOLDS IN SAID BELLOWS BETWEEN SAID RIGIDIZING 